The invention relates to a pixel rounding method for displaying on a screen of a raster scan display device, a plurality for information pixels, each of which is represented by a respective digital code stored in a display memory, said digital codes being accessed repeatedly to display the information pixels in a recurrent cycle of scanning lines, with each row of information pixels being displayed twice in adjacent scanning lines.
Hereinafter, the display comprising such a quantity of pixel information will be referred to as a "display page". The scanning technique which is employed can be a line sequential frame scan or an interlaced two-field scan, provided that each line of pixels is displayed twice in adjacent scanning lines of the raster scan.
In a data display arrangement of the above type, the stored digital codes can be in so-called "bit-map" form comprising at least one information bit in respect of each of the pixels which are to be displayed on the screen of the display device by the scanning action. These information bits are read out in synchonism with the scanning action in such manner as to display successive rows of pixels of the display twice, either in the same scanning lines of the scanning cycle in each field in the case of an interlaced two-field scan, or in successive pairs of scanning lines of the scanning cycle in the case of a line sequential frame scan. The information bits which are read out are applied to a display generator which is responsive thereto to produce a video signal containing the pixel information for driving the display device to produce the "bit-map" display.
Alternatively, in a data display arrangement of the above type, the stored digital codes can be in so-called "character based" form. For the alternative, there is provided, e.g. in the display generator, a store of standard character shapes comprised by patterns of bits, and the codes stored in the display memory are read out recurrently during the scanning action to identify selected character shapes whose bit patterns are read out progressively to be formed into the video signal for driving the display device. The successive rows of pixels which in this instance define the shapes of the displayed characters are displayed twice, as before, to produce in this instance a "character based" display.
A typical character format is a co-ordinate matrix composed of 35 discrete dots arranged in 7 rows and 5 columns, each dot of a character representing a respective bit of the relevant bit pattern.